The invention relates to a method and an apparatus for determining the binder content of bituminous building materials, especially asphalts, wherein a sample of the building material is weighed, the binder is removed from the sample, the sample is reweighed, and the binder content is determined from the weight loss of the sample due to removal of the binder.
The development of such methods is a result of the scarcity of raw materials which has been constantly increasing in recent times, and of the often great amount of unusuable scrap material. In road building there has often been a call for reusing old paving material in the improvement of old pavements or in the production of new pavements, for example by adding to the usual fresh mixtures of rock (e.g., basalt, sand or the like), additive materials or fillers (e.g., limestone) and binders (pure bitumen, as a rule), and preparing hot asphalt concrete together with them in a special drying and mixing apparatus (DE-OS 3,616,995).
A bituminous material made by adding old material must satisfy the same quality requirements as one made without the addition of old material. To be able to satisfy these requirements it is necessary to know the composition of the old material as regards its binder content, the grain size distribution and the content of additives, since only then can the proportions of the fresh starting materials on the one hand and of the old material on the other be precisely controlled.
In one known method of the kind described above, the removal of the binding agent from the sample is performed by extraction with a solvent. The time required for such analysis is quite long, and is unacceptable, especially for the analysis of large samples of about one to five kilograms. Besides, the use of solvents is undesirable for environmental reasons. If the analysis of the binder content, however, is performed using a neutron probe in the likewise-known isotope determination, the binder content can indeed be determined in a very short time. Unlike the extraction method, however, isotope determination does not result in any automatic separation of the binding agent from the rest of the mineral mix. Therefore the removal of the binder must be performed in an additional step which considerably adds to the total analysis time, since otherwise the next-following sieve analysis of the rock mixture to determine the grain-size distribution, which cannot be performed prior to the separation of the binder component, would not be possible. Also, problems would arise in case the determination of the content of additives would have to be performed, for example, by sedimentation.